This invention relates to a method for manufacturing and installing a plurality of flat tension members in an elevator system and to an elevator system having a plurality of flat tension members or belts.
Conventional traction elevator systems typically include a passenger car, a counterweight, two or more tension members or belts interconnecting the car and counterweight, a traction sheave to move the tension members, and a machine to rotate the traction sheave. The machine may be geared or gearless and the tension members may be round.
Flat tension members are defined as having an aspect ratio of greater than one, where the aspect ratio is defined as the ratio of tension member width w to thickness t (Aspect Ratio=w/t). The actual surface of the flat tension member is not necessarily flat. The term flat tension member refers to any rope having as aspect ratio greater than one.
The tension members normally fit within a groove located on the sheave. The grooves have a surface complementary to that of the belt interfacing with the sheave.
Flat tension members as described in PCT publication WO 00/37,738 consist of a plurality of load carrying cords formed from high tensile strength material encased within a coating such as thermoplastic polyurethane. The cords are constructed of high tensile strength fibers such as twisted steel or aramid strands, which are in turn constructed of twisted steel or aramid wires.
The flat tension members represent an improvement over round cables in that they offer reduced rope pressure and increased flexibility, which allows for smaller sheaves.
However, the flat tension members are not perfectly uniform along their length or cross section. There are slight variations that occur along the length of the belt such as saber, which is a curvature of the belt, and taper which is a lateral dimensional variation. Saber and taper cause the flat belts to track (move) either left or right across the sheave groove.
The cordage helix angle, which is the left or right design angle of the twist of the steel or aramid fibers in the cords and the cordage residual torque, which is the twisting force created during manufacturing, also cause the flat tension members to track either right or left across the grooves of the sheave.
Elevator systems commonly comprise multiple belts running in parallel within grooves over the sheave. During installation the sheave is aligned to cause the flat tension members to track within the center of the individual grooves of the sheave to minimize wear on the belts caused by friction, and pressure, which reduce belt life. However, alignment is especially difficult when the individual belts track in opposite directions at the same time. This dictates a sheave design with sufficient margin to account for tracking errors, resulting in increased sheave size.
Therefore there exists a need to improve the method of manufacture and installation to reduce the effects of tracking.
There further exists an improved method of manufacture and installation to reduce sheave size.
There further exists a need for an improved elevator system having a reduced sheave size.
In view of the foregoing disadvantages inherent in the conventional methods and systems in the prior art, the present invention provides for an improved method of manufacturing and installing flat tension members in an elevator system to minimize the effects of tracking to allow for a reduced sheave size.
To accomplish this goal, the present invention incorporates a mark or multiple marks on or in a surface of the flat tension member. The mark indicates the direction of manufacture of the belt.
The belts are then installed in the elevator system by observing the direction indicated by the mark such that all belts are installed in the same direction. The sheave is then aligned such that each belt tracks in the middle of its associated groove. By installing the belts in the same direction, the belts will tend to track left and right across the sheave together, minimizing the total tracking error at any one time. This also simplifies alignment of the sheave to minimize tracking error. Reduction of the total tracking error also allows for reduced sheave size.
In a further embodiment of the invention, the marks are applied at a known point of manufacture of the belt, which is a known distance from an end of the belt. The belts are then installed in the elevator system by aligning the marks such that the belts are installed in the same direction and the corresponding points of manufacture along the belt are aligned. The sheave is then aligned such that the each belt tracks in the middle of its associated groove. In this embodiment the belts are not only aligned in the same direction but each point on belt is also aligned to further ensure that the tracking differences between the belts is minimized.
In yet a further embodiment, the marks are repeated at known intervals. The method and system described herein improves upon the prior art by reducing tracking errors associated with the use of flat tension members in elevator systems. The elimination of such errors improves the life of the belts, reduces sheave size, and reduces installation time.